Brazing structure and metallized structure

ABSTRACT

A structure comprising silicon-containing ceramic body and an active metal-containing metal layer as a brazing layer or a metallization layer bonded to and disposed on the surface of the ceramic body. A reaction layer of a compound containing constituent elements of the ceramic body and the active metal is formed in the interface between the ceramic body and the metal layer. The reaction layer is present ahead the outer circular edge of the metal layer. In particular, when the ceramic body is silicon nitride with the active metal being titanium, the reaction layer comprises a first reaction layer composed mainly of titanium nitride and a second reaction layer composed mainly of titanium silicide. The first reaction layer is present ahead the outer circular edge of the second reaction layer. According to the brazed structure and the metallized structure, the characteristics of the metal layer containing the active metal, such as bonding strength, can be improved with good reproducibility.

TECHNICAL FIELD

The present invention relates to a brazed structure and a metallizedstructure in which a substrate is ceramic material containing Si such assilicon nitride and a brazing layer or a metallization layer containingan active metal is bonded to and disposed on the ceramics.

BACKGROUND ART

Ceramic body such as silicon nitride, SIALON and silicon carbide hasvarious kinds of characteristics not existing in material such asmetals. Due to the above, these have been applied and developed asmaterials of various kinds of components. For instance, by making use ofsuch characteristics as heat resistance, abrasion resistance and lightweight and high mechanical strength, these have been applied instructural and mechanical components. However, ceramic material isinherently brittle. In order to complement such a disadvantage, theceramic material is generally bonded to and integrated with metallicmaterial to use.

In bonding together ceramics and metal, brazing material (active metalbrazing material) containing an active metal such as, for instance,Ag—Cu—Ti alloy is used to form in advance an active metal-containingbrazing layer on a ceramic body. An active metal-containing brazinglayer, after disposing a laminate of respective metal foils, an alloyfoil or alloy powder on a silicon nitride, is formed by heat-treatmentat temperatures higher than the melting point of the activemetal-containing brazing material.

On the other hand, the ceramic material such as silicon nitride, bymaking use of properties of high electrical insulation, high thermalconductance and high mechanical strength thereof, is applied inelectronic components. In this case, with the purpose of forminginterconnection layers and circuit networks, a metal layer(metallization layer) containing an active metal such as Ag—Cu—Ti alloyis formed on the surface of ceramic body (substrate). Such ametallization layer is formed as identical as the brazing layer isformed. When a metal plate such as copper plate is used for theinterconnection layer, an active metal-containing metal layer is usedfor a brazing layer as well as structural material.

When an active metal-containing metal layer (brazing layer ormetallization layer) is formed on a surface of a silicon nitride or thelike, in the existing procedure, it is general to heat-treat underconditions. Under the conditions, active metal-containing brazingmaterial or metallization material sufficiently wets and spreads on thesurface of the silicon nitride.

However, under the existing condition of heat-treatment, there are caseswhere bonding strength of the brazing layer or metallization layer,further the mechanical strength after brazing become insufficient. Thisis due to the existing condition of heat-treatment being set to makesmall a contact angle (wetting angle) of a metal layer by payingattention to wettability of the metal layer to mainly silicon nitride orthe like. According to experiments of the present inventors, it has beenmade clear that reactions between a ceramic material such as siliconnitride and a metal layer must be fully taken into consideration. Due tothe lack of consideration to such points, the existing condition ofheat-treatment tends to cause the decrease of bonding strength of thebrazing layer or metallization layer.

Further, when an active metal-containing metal layer such as Ag—Cu—Tialloy is formed on a silicon nitride through heat-treatment, it is knownthat the silicon nitride and the Ag—Cu—Ti alloy react to form reactionproducts such as TiN for instance at the interface thereof. However, itis not tried to control reaction products considering diffusion andwettability of the metal layer.

As described above, in the existing method of forming an activemetal-containing metal layer (brazing layer or metallization layer),there are problems. These problems are that bonding strength betweenceramic body containing silicon such as silicon nitride, SIALON andsilicon carbide and a metal layer, further the strength after brazingwhen a metal layer being a brazing layer, may be insufficient. From theabove, it is desired, without deteriorating diffusivity (wettability) ofatoms in a metal layer to a ceramic body containing silicon, to improvethe bonding strength or the like of the active metal-containing metallayer as brazing layer or metallization layer with reproducibility.

An object of the present invention is to provide a brazed structure anda metallized structure that enable to improve characteristics such asthe bonding strength or the like of an active metal-containing metallayer with reproducibility.

DISCLOSURE OF INVENTION

A brazed structure of the present invention comprises a ceramic bodycontaining silicon, an active metal-containing brazing layer, and areaction layer. The active metal-containing brazing layer is bonded toand disposed on a surface of the ceramic body. The reaction layer isformed at the interface of the ceramic body and the brazing layer andconsisting essentially of a compound containing constituent elements ofthe ceramics and the active metal. Here, the reaction layer exists aheada front edge line of the brazing layer along a direction into which thebrazing layer spreads while wetting.

A metallized structure of the present invention comprises ceramic bodycontaining silicon, an active metal-containing metallization layer, anda reaction layer. The active metal-containing metallization layer isbonded to and disposed on a surface of the ceramic body. The reactionlayer is formed at the interface between the ceramic body and themetallization layer and consisting essentially of a compound containingconstituent elements of the ceramic body and the active metal. Here, thereaction layer exists ahead a front edge line of the metallization layeralong a direction into which the metallization layer spreads whilewetting.

In a brazed structure and a metallized structure of the presentinvention, in more specific, the reaction layer comprises a firstreaction layer, and a second reaction layer. The first reaction layerexists more close to the ceramic body than to the brazing layer andconsists mainly of a compound made of a non-metallic element ofconstituent of the ceramic body and an active metal. The second reactionlayer exists more close to the brazing layer than to the ceramic bodyand consists mainly of a compound made of silicon of constituentelements of the ceramic body and an active metal. In the case of thereaction layer having such a structure, the first reaction layer existsahead of a front edge line of the second reaction layer, or the firstreaction layer is formed uniformly.

In a brazed structure and a metallized structure of the presentinvention, for the ceramic body, one kind selected from, for instance,silicon nitride, SIALON and silicon carbide can be used. In addition, asthe active metal, at least one kind selected from, for instance,titanium, zirconium, hafnium, niobium, aluminum, vanadium and tantalumcan be used.

In the present invention, a reaction layer consisting of compoundscontaining constituent elements of the silicon-containing ceramic bodyand an active metal exists ahead a front edge line of a metal layer asthe brazing layer or the metallization layer. Thus, by allowing areaction layer consisting of compounds that are reaction products of theceramic body and an active metal to exist ahead in a direction intowhich the metal layer spreads while wetting (diffusing direction), thebonding strength of the metal layer can be improved with stability.

In particular, by advancing the first reaction layer ahead of the secondreaction layer, the metal layer bonded with high strength can berealized with good reproducibility. The first reaction layer largelycontributes in improvement of the bonding strength of the ceramic bodyand the metal layer and consists mainly of a compound of a nonmetallicelement of the ceramic body and an active metal such as titaniumnitride. The second reaction layer consists mainly of a compound ofsilicon and an active metal such as titanium silicide. Further, even byforming the first reaction layer uniform, the metal layer bonded withhigh mechanical strength can be obtained with good reproducibility. Whenthe second reaction layer advances ahead of the first reaction layer,titanium nitride or the like that is a main component of the firstreaction layer decreases in its amount. As a result of this, the firstreaction layer is likely to be formed discretely to result indeterioration of the bonding strength.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-section showing schematically a bonded structure ofceramics and a metal layer as one embodiment of a brazed structure and ametallized structure of the present invention,

FIG. 2 is an enlarged cross-section showing an essential portion of abonded structure of the ceramics and metal layer shown in FIG. 1,

FIG. 3 is a diagram showing a change with time of contact angle andwetting radius of molten Ag—Cu—Ti alloy layer to silicon nitride,

FIG. 4 is a cross-section showing an interface structure formed based onanother heat-treatment process of a bonded structure of the ceramic andmetal layer illustrated in FIG. 1,

FIG. 5 is a diagram showing schematically an observed result of across-section of a bonded structure of silicon nitride/metal layeraccording to Embodiment 1 of the present invention,

FIG. 6 is a diagram showing schematically an observed result of across-section of a bonded structure of silicon nitride/metal layeraccording to Embodiment 2 of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

In the following, embodiments for carrying out the present inventionwill be described.

FIG. 1 is a cross-section showing schematically a bonded structure of aceramics and a metal layer as one embodiment of a brazed structure and ametallized structure of the present invention. The bonded structure 1 ofa ceramics and a metal layer shown in the figure has a structure inwhich a metal layer 3 is bonded to and disposed on a surface of ceramicmaterial 2.

For the ceramic body 2, various kinds of ceramic body containing silicon(Si) as a main constituent element can be used. In specific, siliconnitride (Si₃N₄), SIALON (Si—Al—O—N), silicon carbide (SiC) or the likecan be applied.

These ceramic bodies 2 are not particularly restricted in theircompositions and manufacturing methods. The ceramic body containing Siof various kinds of compositions and manufacturing methods can be used.For instance, for the silicon nitride, ones that are produced by the useof various kinds of sintering methods with various kinds of metal oxidessuch as yttria, alumina, magnesia and so on or nitrides of metals assintering aid can be used. The various kinds of sintering methodsinclude pressureless sintering, gas-pressured sintering, hot pressing,reaction sintering and so on. In addition, ones treated by use of HIP orthe like also can be used.

When a bonded structure 1 of ceramics/metal layer is used as a brazedstructure, for the ceramic body 2, various kinds of sintered bodies forstructural materials or electronic materials can be used. For theceramics for structural material, mainly, silicon nitride, SIALON andsilicon carbide of which mechanical strength, hardness and toughness areimproved can be preferably used.

Further, when a bonded structure 1 of ceramics/metal layer is used as ametallized structure, for the ceramic body 2, silicon nitride substrate,SIALON substrate, silicon carbide substrate or the like for electronicuse can be used. For the silicon nitride substrate for electronic use,silicon nitride substrate of which thermal conductivity and insulationare considered of importance can be used. In addition, a silicon carbidesubstrate that functions as a semiconductor substrate can be also used.

On the ceramic body 2, a metal layer (hereinafter refers to as activemetal containing metal layer) 3 containing an active metal is formed asan active metal brazing layer or metallization layer. For the activemetal containing metal layer 3, metal layer forming material to whichactive metals such as, for instance, Ti, Zr, Hf, Nb, Al, V, Ta or thelike are added can be used. As the base material of the metal layerforming material, Ag—Cu alloy, Cu or the like can be cited.

The active metals as described above are preferable to be contained inthe metal layer forming material in the range of approximately 1 to 10%by weight. When the content of the active metal is less than 1% byweight, the amount of formation of a compound as a reaction layer thatwill be described later in detail becomes insufficient. As a result ofthis, the bonding strength with the ceramic body 2 containing Si can notbe sufficiently high. on the other hand, when the content of the activemetal exceeds 10% by weight, the amount of compound layer increases somuch to cause a likelihood of deteriorating the bonding strength.

Among these, particularly Ag—Cu—Ti alloy containing Ti as an activemetal can be preferably used. The Ag—Cu—Ti alloy has an excellentfunction for either of a brazing layer and a metallization layer. Inaddition, Ti as the active metal, being excellent in reactivity inparticular with silicon nitride and SIALON, largely contributes inimproving the bonding strength of the ceramic body 2 and the activemetal containing metal layer 3.

The active metal containing metal layer 3 can be formed in the followingway. First, an alloy foil or alloy powder containing principal formationmaterial of the metal layer and active metal, or a laminate of therespective metal foils is disposed on the ceramic body with a desiredshape. Thereafter, at temperatures of melting point of the employedactive metal containing metallic material or more, heat-treatment iscarried out to form the active metal containing metal layer 3. Duringsuch heat-treatment, the active metal containing metallic material ismelted to diffuse along the surface of the ceramic body 2 (spread whilewetting).

As the wetting of the active metal containing metallic materialproceeds, the active metal diffuses and begins to react with the ceramicbody 2 containing Si. As a result, at the interface of the ceramic body2 and active metal containing metal layer 3, a reaction layer 4consisting of compounds containing the constituent elements of theceramic body 2 and the active metal is formed. At this time, theheat-treatment is carried out under the following condition. Thecondition is that relative to a direction (wetting and spreadingdirection: shown with an arrow mark in FIG. 2) in which the active metalcontaining metal layer 3 diffuses, a compound layer as a reaction layer4 advances ahead of the front edge line of the active metal containingmetal layer 3.

That is, the reaction between the ceramics 2 and active metal is made toadvance in a direction of the surface of the ceramic body 2 than thefront edge line of the active metal containing metal layer 3. In otherwords, the reaction products containing the constituent elements of theceramic body 2 and the active metal are grown in the direction of thesurface. Then, on the reaction layer 4 consisting of compounds formedbased on the reaction and growth, the active metal containing metallayer 3 is made to diffuse.

Thereby, finally, as shown in FIG. 1, the reaction layer 4 consisting ofcompounds that contain the constituent elements of the ceramic body 2and the active metal is formed in a state of advancing ahead the frontedge line of the active metal containing metal layer 3. By controllingthe reaction of the ceramic body 2 and active metal, the aforementionedstate can be obtained.

As mentioned above, the reaction layer 4 consisting of compoundscontaining the constituent elements of the ceramic body 2 and the activemetal is advanced ahead of the front edge line of the active metalcontaining metal layer 3. Thereby, there always exists a reaction layerbetween the ceramic body 2 and active metal containing metal layer 3.Further the amount of formation and state of formation of the compoundsas the reaction products can be stabilized.

The bonding state of the edge of the active metal containing metal layer3 and the ceramic body 2 particularly affects on the bonding strength ofthe ceramic body 2 and the active metal containing metal layer 3.Accordingly, the reaction layer 4 is made to advance ahead of the frontedge line of the active metal containing metal layer 3 to stabilize thestate of the compounds as the reaction products between the edge of theactive metal containing metal layer 3 and the ceramic body 2. Thereby,the active metal containing metal layer 3 can be prevented from peelingoff the edge thereof. Therewith, the bonding strength of the ceramicbody 2 and the active metal containing metal layer 3 can be increasedwith good reproducibility.

In an existing bonded body of ceramics/metal layer, an active metal andceramic body is made to react only at the interface of the ceramics andthe active metal containing metal layer. In that case, themicrostructure of the reaction layer is likely to fluctuate particularlyat the edge of the metal layer. On the contrary, by advancing thecompound layer as the reaction layer 4 ahead of the front edge line ofthe active metal containing metal layer 3, the bonding state of theactive metal containing metal layer 3, in particular of the edge thereofcan be stabilized with good reproducibility.

In other words, so far a triple point of ceramic body/active metalcontaining metal layer/atmosphere is a starting point of reaction. Onthe other hand, in the present invention, the neighborhood of the edgeof the active metal containing metal layer 3 is constituted of a triplepoint and the reaction layer 4 of a thickness of several tens nmpreceding thereof. Here, the triple point is constituted of active metalcontaining metal layer 3/reaction layer 4 (compound layer)/atmosphere.Thereby, the neighborhood of the edge of the active metal containingmetal layer 3 is made to stabilize. Accordingly, the bonding strengthbetween the ceramic body 2 and active metal containing metal layer 3 canbe increased with good reproducibility.

Next, the compound layer as reaction layer 4 will be described indetail. By the way, in the following, silicon nitride is used as theceramic body 2 and Ti is used as the active metal.

In such a case, as shown in FIG. 2, on the side closer to the siliconnitride 2, a first reaction layer 5 containing titanium nitride (TiN) asa principal component is formed. And, on the side closer to the activemetal containing metal layer 3 a second reaction layer 6 containingtitanium silicide (for example Ti₅Si₃) as a principal component isformed. Thus, at the interface of the silicon nitride 2 and the activemetal containing metal layer 3, a compound layer of two-layeredstructure (reaction layer 4) is formed. The compound layer is formedbased on the reaction of Si and N that are constituent elements of thesilicon nitride 2 and an active metal.

When the activity of Ti atoms that spreads through, for instance,surface diffusion from the active metal containing metal layer 3 ishigh, titanium nitride is preferably formed. Accordingly, at the siliconnitride 2 side that is a reaction point, a first reaction layer 5containing titanium nitride as a principal component is formed. On theother hand, on the active metal containing metal layer 3 side, a secondreaction layer 6 containing titanium silicide that is a stable phase asa principal component is formed. Among these reaction products, titaniumnitride, compared with titanium silicide, contributes more largely inimproving the bonding strength between the silicon nitride 2 and theactive metal containing metal layer 3.

Accordingly, in a bonded structure 1 of silicon nitride/metal layerhaving a reaction layer 4 of two-layer structure, as shown in FIG. 2, afirst reaction layer 5 of which principal component is titanium nitrideis preferable to advance ahead of a second reaction layer 6 of whichprincipal component is titanium silicide. In other words, the firstreaction layer 5 of which principal component is titanium nitride ispreferable to be formed in a larger amount.

The state in which the first reaction layer 5 advances ahead of thesecond reaction layer 6 can be obtained by controlling theheat-treatment period of the metal layer forming material containing Ti.FIG. 3 shows a change with time of the contact angle of the Ticontaining metal layer (in specific, Ag—Cu—Ti alloy) 3 with the siliconnitride 2 and a radius (wetting radius) in a spreading direction whilewetting. As obvious from FIG. 3, the increase rate (that is, diffusionrate) of the wetting radius is high in the first stage (I) of, forinstance, approximately 250 sec or less from the start of wetting, anddecreases drastically thereafter in the second stage (II). On the otherhand, the contact angle, while decreasing drastically in the first stage(I), still continues to decrease in the second stage (II).

Of the respective stages (I) and (II) of the heat-treatment like this,in the first stage (I) where the wetting radius of the Ti containingmetal layer 3 increases drastically, large amount of Ti atoms diffusesfrom the Ti containing metal layer 3 at the position preceding the frontedge line of the Ti containing metal layer 3 in the wetting direction ofthe Ti containing metal layer 3. That is, the activity of Ti diffusingthereto through surface diffusion is high and titanium nitride is formedin sufficient amount due to the reaction of Ti and the silicon nitride2. In addition, the titanium nitride is uniformly formed.

By stopping the heat-treatment at such first stage (I) the state inwhich the first reaction layer 5 advances ahead of the second reactionlayer 6 can be obtained. Even if the heat-treatment is finished at thefirst stage (I), as mentioned above, since the Ti containing metal layer3 diffuses (spreads while wetting) sufficiently in the first stage (I),defect due to insufficiently formed area of the Ti containing metallayer 3 is never caused.

On the other hand, after the first stage (I) when the heat-treatment isfurther continued to enter into the second stage (II), the contact angle(wetting angle) of the Ti containing metal layer 3 becomes smaller thanthat of after the first stage (I). However, as the wetting proceeds(proceeding of reaction), Ti atoms in the melt is consumed to decreasethe activity of Ti. As a result, titanium silicide is likely to form.That is, as shown in FIG. 4, the second reaction layer 6 of whichprincipal component is titanium silicide goes ahead of the firstreaction layer 5.

As titanium silicide is formed, titanium nitride becomes difficult togrow and the first reaction layer becomes discrete. It is understoodfrom a viewpoint of the thermodynamics that as the activity of Tidecreases, the stable phase converts from titanium nitride (TiN) totitanium silicide (for instance Ti₅Si₃). The activity of Ti decreases asthe wetting period increases and the preceding layer switches from thefirst reaction layer 5 of which principal component is titanium nitrideto the second reaction layer 6 of which principal component is titaniumsilicide.

As mentioned above, by advancing the first reaction layer 5 ahead of thesecond reaction layer 6, due to titanium nitride, an improvement of thebonding strength between the silicon nitride 2 and the Ti containingmetal layer 3 can be obtained with more stability. In other words, thefirst reaction layer 5 of which principal component is titanium nitrideis formed in a larger quantity and the titanium nitride is formeduniformly. Thereby, the improvement of the bonding strength between thesilicon nitride 2 and the Ti containing metallic layer 3 can be realizedwith more stability. In such a structure of reaction layer, the bondingstrength between the silicon nitride 2 and the Ti containing metal layer3 can be increased further and the reproducibility of such bondingstrength can be remarkably improved. In addition, the consumption of Tiatoms necessary for bonding in the later process can be suppressed.

In the explanation of morphology of the aforementioned compound layer 4of two-layered structure, Ti is taken as an active metal forexplanation. However, even when other active metals are used, the firstreaction layer can be advanced ahead of the second reaction layer. Evenin such a case, by advancing a reaction layer mainly containing areaction product having high activity ahead of the other reaction layer,the bonding strength of a silicon nitride 2 and an active metalcontaining metal layer 3 can be further increased.

In addition, also when another ceramics than the silicon nitride, forinstance, SIALON or silicon carbide is used as ceramic body 2, the samecan be said. When SIALON is used as the ceramic body 2, the reactionsapproximately identical with the case of silicon nitride can beexpected. When silicon carbide is used as the ceramic body 2, a firstreaction layer is formed on the side closer to the substrate and asecond reaction layer is formed on the side closer to the metal layer.Here, the principal components of the first reaction layer and secondreaction layer are titanium carbide (TiC) and titanium silicide(Ti₅Si₃), respectively. The reaction layer of which principal componentis titanium carbide, though formed in a smaller quantity than titaniumnitride, behaves approximately identical with titanium nitride.

As mentioned above, the reaction layer 4 formed at the interface of theceramic body 2 containing Si and the active metal containing metal layer3 comprises a first reaction layer 5 and a second reaction layer 6.Here, the first reaction layer 5 comprises a compound of a non-metallicelement (N or C) of constituent elements of the ceramic body 2 and anactive metal as the principal component. The second reaction layer 6comprises a compound of Si among constituent elements of the ceramicbody and an active metal as the principal component.

When having such a structure of reaction layer, the first reaction layer5 can be made to advance ahead the front edge line of the secondreaction layer 6 along a direction in which the active metal containingmetal layer 3 spreads while wetting. Thereby, the bonding strengthbetween the ceramic body 2 and the active metal containing metal layer 3can be further increased, and such bonding strength can be remarkablyimproved in reproducibility thereof. Further, by forming the firstreaction layer uniformly, similarly, the bonding strength andreproducibility thereof can be increased remarkably.

When a bonded structure 1 of ceramics/metal layer of this embodiment isused as a brazed structure, the bonding strength of the active metalcontaining metal layer 3 as a layer of active metal brazing material tothe ceramic body 2 can be increased with good reproducibility.Accordingly, not only reliability of the active metal containing brazinglayer but also the strength and reliability of a bonded body that isproduced in the later brazing process can be remarkably improved.Further, when the bonded structure 1 of ceramic body/metal layer is usedas a metallized structure, reliability of the metallization layer asinterconnection layer, electrode and parts mounting portion can beremarkably improved.

Next, specific embodiments of the present invention and results thereofwill be described.

Embodiments 1 and 2

First, on a silicon nitride an alloy of a composition of 67.7% by weightof Ag-27.4% by weight of Cu-4.9% by weight of Ti is disposed to melt byheating in a vacuum lower than 10⁻³ Pa. The heating is carried out attemperatures of the melting point of this alloy that is 1183 K or more.Samples for observation are prepared by cooling after holding 60 sec(Embodiment 1) and 900 sec (Embodiment 2) from the start of wetting,respectively.

The triple points of these samples are observed from the surface with asecondary ion microscope (SIM) and the cross-sectional structure aroundthe triple point is observed with a transmission electron microscopewith a cold emission gun (FE-TEM). In addition, the compositions of therespective layers are analyzed by use of an energy dispersive X-rayspectroscopy (EDS) method. Further, in order to compare the change ofthe existing macroscopic wetting behavior and the change of thecomposition of the triple point, the change of the contact angle andwetting radius of Ag—Cu—Ti alloy with time is also measured. Themeasurement results are shown in FIG. 3.

First, by SIM, it is confirmed that a reaction layer forms ahead of thetriple point of metal/substrate/gaseous phase. These preceding layersare observed in the respective samples of embodiments 1 and 2. Thoughthe triple line of metal/substrate/gas phases have wavy formsmicroscopically, the front line of the preceding layer is almoststraight. On the basis of the morphology of these lines, the precedinglayers are not considered to form due to the contraction of metal in thecourse of cooling. But these are considered to form due to the growth ina lateral direction of a reaction product during wetting processoverrunning the triple line of metal/substrate/gas phases. Thecontraction of metals is an isotropic phenomenon. Accordingly, such wavytriple lines are not formed. In addition, from their morphology, thereaction layer is considered to be very thin.

FIG. 5 shows schematically an observed result (TEM photograph) of across-section around the triple point of a sample according toEmbodiment 1. FIG. 6 shows schematically an observed result (TEMphotograph) of a cross-section around the triple point of a sampleaccording to Embodiment 2. As shown in FIGS. 5 and 6, it is observedthat the reaction layers (compound layers) of the respective samples goahead of the triple point, that is, the front edge line of the activemetal containing metal layer. By realizing such states, the bondingstrength of the metal layer and the bonding strength after brazing canbe increased.

Further, in FIGS. 5 and 6, in both samples, at the interface of Si₃N₄and the metal layer, a reaction layer of two-layered structure is foundto form. From the element and mass analysis using EDS, the upper and thelower layers are confirmed to be a Ti₅Si₃ layer 6 and TiN layer 5,respectively. The TiN layer 5 is composed of nano-particles of TiN.However, whereas in embodiment 1 where the heat-treatment period is setshorter, the TiN layer 5 goes ahead the Ti₅Si₃ layer 6, in embodiment 2where the heat-treatment period is set longer, on the contrary, it isfound that Ti₅Si₃ layer 6 advances ahead of TiN layer 5.

As obvious from FIG. 3, as the wetting period becomes longer, the Ti₅Si₃layer 6 advances more preferentially. This is considered that as thewetting proceeds, Ti in the melt is consumed to cause decrease of theactivity of Ti. As the activity of Ti decreases, it is considered thatthe stable phase converts from TiN to Ti₅Si₃. The activity of Tidecreases as the increase of the wetting period and the preceding layerconverts from TiN to Ti₅Si₃.

The bonding strength between Si₃N₄ and the metal layer is larger inembodiment 1 where TiN layer 5 is formed uniformly and TiN layer 5 goesahead of Ti₅Si₃ layer 6. Further, the sample of embodiment 1, beingsuppressed in consumption of Ti atoms necessary for bonding of the laterprocess for example, can further heighten the brazing strength. When themetal layer is a metallization layer, the similar effects can beexpected.

INDUSTRIAL APPLICABILITY

A brazed structure of the present invention largely enhances not onlyreliability of an active metal containing brazing layer but alsostrength and reliability of a bonded body to be fabricated in the laterbrazing process. Accordingly, it is useful upon manufacturing variouskinds of bonded bodies. In addition, a metallized structure of thepresent invention largely enhances reliability of a metallization layerto be used as for instance interconnections or circuit networks.Accordingly, it is useful for production of various kinds of electronicdevices.

What is claimed is:
 1. A brazed structure, comprising: a ceramic bodycontaining silicon; a brazing layer containing an active metal bonded toand disposed on a surface of the ceramic body; and a reaction layerconsisting essentially of a compound containing a constituent element ofthe ceramic body and the active metal formed at an interface of theceramic body and the brazing layer, the reaction layer comprising afirst reaction layer containing a compound of a non-metallic element ofthe constituent elements of the ceramic body and the active metal as aprincipal component and existing on a side closer to the ceramic bodythan to the brazing layer, and a second reaction layer containing acompound of the silicon of the constituent elements of the ceramic bodyand the active metal as a principal component and existing on a sidecloser to the brazing layer than to the ceramic body; wherein thereaction layer exists ahead of a front edge line of the brazing layeralong a direction in which the brazing layer spreads while wetting, andthe first reaction layer exists ahead of a front edge line of the secondreaction layer along the direction.
 2. The brazed structure as set forthin claim 1: wherein the ceramic body is one kind selected from siliconnitride, SIALON and silicon carbide.
 3. The brazed structure as setforth in claim 1: wherein the active metal is at least one kind selectedfrom Ti, Zr, Hf, Nb, Al, V and Ta.
 4. The brazed structure as set forthin claim 1: wherein the first reaction layer is uniformly formed.
 5. Thebrazed structure as set forth in claim 1: wherein the ceramic body issilicon nitride, and the active metal is titanium.
 6. The brazedstructure as set forth in claim 5: wherein the first reaction layercontains titanium nitride as a principal component, and the secondreaction layer contains titanium silicide as a principal component.
 7. Ametallized structure, comprising: a ceramic body containing silicon; ametallization layer containing an active metal bonded to and disposed ona surface of the ceramic body; and a reaction layer consistingessentially of a compound containing a constituent element of theceramic body and the active metal formed at an interface of the ceramicbody and the metallization layer, the reaction layer comprising a firstreaction layer containing a compound of a non-metallic element of theconstituent elements of the ceramic body and the active metal as aprincipal component and existing on a side closer to the ceramic bodythan to the metallization layer, and a second reaction layer containinga compound of the silicon of the constituent elements of the ceramicbody and the active metal as a principal component and existing on aside closer to the brazing layer than to the ceramic body; wherein thereaction layer exists ahead of a front edge line of the metallizationlayer along a direction in which the metallization layer spreads whilewetting, and the first reaction layer exists ahead of a front edge lineof the second reaction layer along the direction.
 8. The metallizedstructure as set forth in claim 7: wherein the ceramic body is one kindselected from silicon nitride, SIALON and silicon carbide.
 9. Themetallized structure as set forth in claim 7: wherein the active metalis at least one kind selected from Ti, Zr, Hf, Nb, Al, V and Ta.
 10. Themetallized structure as set forth in claim 7: wherein the first reactionlayer is uniformly formed.
 11. The metallized structure as set forth inclaim 7: wherein the ceramic body is silicon nitride and the activemetal is titanium.
 12. The metallized structure as set forth in claim11: wherein the first reaction layer contains titanium nitride as aprincipal component, and the second reaction layer contains titaniumsilicide as a principle component.